This invention relates to a process intended to control the perpendicularity of plane faces of a cylindrical component, relative to the axis of symmetry of this component.
More exactly, the invention concerns a process allowing the measurement of an out-of-true perpendicularity of at least one generator of the component, relative to one of its faces, over a given length of the component.
The process according to the invention can be used in all cases where it is required to carry out a very precise measurement of the perpendicularity of a cylindrical component. A preferred application concerns the control of the perpendicularity of nuclear fuel pellets during their manufacture.
The fuel rods used in nuclear reactors include cylindrical nuclear fuel pellets, mounted end to end in metal sheaths. During the manufacture of the pellets, their size and their geometry, particularly their perpendicularity, must be regularly controlled, so as to verify that they comply fully with the required tolerances.
In existing manufacturing shops, the size of the nuclear fuel pellets is measured with the help of mechanical probes and micrometric measurement means. The precision of the measurements carried out in this way is of the order of 20 xcexcm.
Furthermore the perpendicularity of the circular faces of the pellets, relative to their axis of symmetry, is generally controlled by sounding. To this end, the sampled pellet is usually placed horizontally on rollers which are also horizontal. Rotating the rollers or a pressure roller rotates the pellet. Measurements are then taken by a micrometric probing of one of the two circular faces of the pellets. The precision of the measurements carried out in this way is comparable to that of the size measurements, in other words of the order of 20 xcexcm.
The disadvantages of this usual technique for controlling perpendicularity are that it does not allow pellets with a reduced or non-existent collar to be controlled and that it does not allow pellets of different diameters to be controlled without adaptation.
The object of the invention is to be exact a process for controlling the perpendicularity of a cylindrical component, such as a nuclear fuel pellet, obtaining a precision of measurement substantially greater than existing control techniques, in other words above 8 xcexcm.
A further object of the invention is a process allowing the perpendicularity of cylindrical components of different diameters and of different lengths to be controlled without any modification.
Moreover, the invention concerns a process for controlling the perpendicularity of cylindrical components obtaining measurements which are stable over time and the implementation of which is compatible with the instigation of controls within a glove box.
In accordance with the invention, a process is proposed for controlling the perpendicularity of a plane face of a cylindrical component, relative to an axis of symmetry of said component, characterised in that it includes the steps consisting in:
laying said face of the component on a fixed support plane such that said axis of symmetry passes approximately through a fixed point of reference of said support plane; and
determining optically, in at least one measuring plane a passing through the point of reference and perpendicular to the support plane, an out-of-true perpendicularity of a least one generator of the component, contained in the measuring plane, relative to said face, the out-of-true perpendicularity being determined by measuring optically, at two different levels of the component along its axis of symmetry, the distance separating each generator from a fixed straight line of reference perpendicular to the support plane and contained in the measuring plane, then by calculating the difference between the distances measured at each of the two levels.
In a preferred embodiment of the invention any out-of-true perpendicularity of the two generators of the component, contained in the measuring plane, is determined optically.
In this preferred embodiment, any out-of-true perpendicularity in two measuring planes perpendicular to each other is also determined optically.
In this case, a maximum out-of-true perpendicularity Xmax is calculated to advantage by applying the equation:
Xmax={square root over (X12+X22+L )},
where X1 and X2 represent the greatest out-of-true perpendicularity of the two generators in each of the two measuring planes respectively.
To advantage, the distances at each of the two levels are measured simultaneously by means of at least one pair of laser scanning micrometers provided with emitting slots parallel to the measuring plane, the above mentioned slots emitting laser arrays which cut an axis of reference perpendicular to the support plane, passing trough the point of reference at each of the two levels.
When the measurements are taken in two measuring planes perpendicular to each other, the distances in these two planes are then measured simultaneously, by means of two pairs of laser scanning micrometers.
Each of the laser scanning micrometers used includes to advantage an emitter and a receiver located on either side of the component. The emitter used is provided with the emitting slot and must be placed at a distance of 60xc2x12 mm from the axis of reference. The receiver is aligned with the emitter and placed at a distance of about 95 mm from this axis.
In order for the gap between the 2 levels of measurement to be compatible with the smallest length of the components to be controlled, despite the space taken up by the micrometers, the two micrometers of each pair of micrometers are placed to advantage such that the laser arrays emitted by their emitting slots are respectively parallel to the support plane and inclined relative to this plane.
In the preferred embodiment of the invention, on the support plane, for each pair of micrometers next to and at a distance from the component, is mounted a rod of reference of which the generator, turned towards the component and located in the measuring plane, substantiates the straight line of reference. More exactly, each rod of reference is mounted to advantage at the same distance from the emitter as the axis of reference.
To ensure good reproducibility of the measurements, the support plane is to advantage substantiated by three support zones, evenly distributed around the point of reference.
In a preferred application of the invention, the cylindrical components controlled are nuclear fuel pellets.